If we want to print last line of any file, we can use the following code.

use strict;
use warnings;
# open the file using _ to avoid multiple system calls invoked by perl
open _,"filename";
# reading all lines from a file and store it into @lines array
my @lines=<_>;
# printing the last line of a file in @lines by $#lines => last index +of the array
print @lines[$#lines];

This is complete nonsense. Using an underscore as the filename makes no difference to the execution, but makes the code harder to understand. Also, you should normally use lexical filehandles. Lastly, there's no error checking on the open.